workaround for the conflicting types error.

/opt/gcc-arm-none-eabi-4_8-2013q4/lib/gcc/arm-none-eabi/4.8.3/include/stdint-gcc.h:40:24: error: conflicting types for 'int32_t'
 typedef __INT32_TYPE__ int32_t;
                        ^
Add definitions to workaround the error:
u-boot.lds:9: nonconstant expression for origin